Hi Khaled, > unsupported operand type(s) for ** or pow(): ‘AddVariable' and 'int' This is probably something that you can handle by writing explicitly the product. The square is sometimes difficult for the code since it needs to know on which index to contract. > ALOHAERROR : Unable to deal with 4(or more) point interactions > in presence of majorana particle/flow violation This is the error I mentioned before that MG can not handle 4 fermion interaction with fermion flow violation. Cheers, Olivier On 27 Jun 2015, at 18:16, Khaled Teilab